The major task of the visual system is to build a spatial map of the environment: A precise retinotopic map projects an image of the retina onto the optic lobes. We are concerned with the qualitative map built by the Drosophila visual system for color vision and recognition of the vector of polarized light. The rhodopsins expressed in the inner photoreceptors (PR's) R7 and R8 defines functionally distinct ommatidia that are involved in color vision. To address how the visual system integrates information about the quality of light, we offer the following aims: 1. Mutual exclusion of rhodopsins: We will study how Rhodopsin proteins are involved in the process of excluding expression of other rh's in the same cell and what the downstream events are. This function represents a paradigm that might be of interest for other sensory systems that use similar types of receptors. 2. Signaling pathway between R7 and R8: We have isolated a series of mutants that affect the communication between R7 and R8 in opposite ways without affecting R7 rh expression. We will characterize this cascade of genes genetically and molecularly, both in the adult retina and in the larval eye that represents a highly simplified visual system. 3. A behavior assay for color vision: We will develop a behavior assay for color vision. We will use our collection of mutants and appropriate genetic tools to evaluate the function of the different subclasses of ommatidia and analyze new mutants that affect color processing in the medulla. Finally, we will test the role of the two classes of PR's in the larval eye to entrain the circadian clock at different times of day. 4. A new screen to identify mutations affecting rh expression: We have designed an insertional mutagenesis recessive mosaic screen based on a new universal transposable element piggyBac with a different insertional specificity than P-elements. This screen will aid us in cloning genes from the previous screen as well as for identifying new mutants. This system represents a simple paradigm to a basic problem of sensory perception using a very amenable genetic system that has so far not been used for the study of color vision. As the nocturnal mouse model is not appropriate for studying color vision, this places Drosophila in a unique position for such experimental manipulations.